Sleep apnea is characterized by a cessation or reduction of breathing during sleep. Obstructive sleep apnea (OSA) refers to apnea syndromes due primarily to collapse of the upper airway during sleep. It is estimated that 2 to 4% of middle-aged North Americans suffer from obstructive sleep apnea (OSA). Left untreated, sleep apnea is known to cause or aggravate other serious medical conditions, including heart disease, hypertension, and hypoxia. However, because episodes of apnea interrupt sleep, the most noticeable consequences of the untreated condition are fatigue and daytime sleepiness. These conditions are dangerous for individuals practicing a profession requiring alertness, and particularly those professions in which the work may be monotonous. For example, it is believed that OSA has been a contributing factor in numerous traffic accidents involving long-distance truck-drivers.
One frequently prescribed course of treatment for OSA is mandibular advancement therapy. This treatment consists of mechanically positioning the lower jaw (mandible) of the patient forward, and maintaining that position for the duration of sleep. This is accomplished by fitting the patient with a dental appliance, known as a mandibular advancement device (MAD). The MAD is similar in appearance to an orthodontic retainer or a protective mouth-guard, and is manufactured by a qualified dental health care provider. The MAD is typically in two parts: an upper part fitted to the upper teeth, and a lower part fitted to the lower teeth. The relative position of the two parts determines the degree of mandibular advancement. During sleep, the two parts are attached together such that the lower mandible is not able to fall back. On some MADs the relative position is adjustable by the dental health care provider. The American Academy of Sleep Medicine has acknowledged that Mandibular advancement therapy is effective for treating mild to moderate sleep apnea. The anterior mandibular position helps prevent collapse of the soft tissue in the palate which is frequently the cause of obstructive sleep apnea, thus improving the quality of sleep, and consequently, daytime alertness.
For individuals employed in professions where a lack of alertness is a danger to public safety, treatment of obstructive sleep apnea with MAD or other dental appliance therapy may be mandated, either by the employer, a professional association, government body, or insurance provider. Although MAD devices are generally designed with consideration to patient comfort, there is a period where the patient must adjust to the new device, during which therapy is often abandoned due to irritation and discomfort. Thus, mere possession of a treatment device (for example, MAD or other dental appliance) is not sufficient to verify the patient has submitted to treatment recommendations. A recent statement on MADs from the American Trucking Association stated that there is evidence that MADs may help in reducing OSA in individuals with mild to moderate OSA there is no method of measuring compliance. Accurate confirmation of compliance may soon become a requirement for maintaining or renewing qualifications and licenses for some professions, and/or for obtaining reimbursement from a health insurance provider. Thus, there is a need to accurately know when a dental appliance such as a mandibular advancement device is being worn by a patient.
Devices disclosed in DuHamel et al US2010/0152599, Rahman et al US2006/0166157, Longley US2007/0283973, and Ivanov et al. U.S. Pat. No. 5,774,425 typically measure ambient temperature. Discussion of measuring other parameters such as oxygen saturation, light, pressure, movement, etc. are disclosed but methods of how to use these signals to increase accuracy of the oral compliance device are not disclosed.
Typical devices currently available for estimating compliance with MAD therapy and orthodontic treatments are battery-operated electronic devices that record only ambient temperature and are embedded within the oral appliance. These devices typically comprise a thermal sensor, a memory storage device, a battery power supply, a clock and an electronic processor. Such devices must, obviously, be of sufficiently small size to allow for embedding into the oral appliance, and preferably minimally increasing its size, so they do not add to patient discomfort or inhibit the effectiveness of the MAD in treating OSA. This limits the type of signals that may practically be recorded to those that can be measured with sensors having small size and low power consumption.
The simplest such systems record intra-oral temperatures using a suitable sensor (typically a thermistor) to determine whether they are within a range that is consistent with placement in the mouth of a patient.
One article titled “Applicative Characteristics of New Microelectronic sensors Smart Retainer and TheraMon for Measuring Wear Time” that appeared in Journal of Orofacial Orthopedics (Timm Cornelius Schott, Gernot Göz, J Orofac Otrhop (German Orthodontic Society) 2010; 71:339-47) compared the Smart sensor to the TheraMon sensor. This article explained how they tested the devices using a readily obtainable thermostatic water bath, a Buchi B-490 Heating Bath. By programming the water bath to heat the water to a temperature of 35° C. for a specified length of time and then allowing the temperature to fall to room temperature the authors were able to trick both sensors into reporting wear time during the time the water was heated to 35° C. This testing teaches the reader how to fool both the Smart and TheraMon sensors into thinking that they were in the mouth of a patient.
Both the Smart and TheraMon sensors sample a temperature signal once every 15 minutes. The Smart chip has a sensitivity of 0.3° C. and the TheraMon had a 0.1° C. In the article, the authours discuss that the TheraMon chip was more accurate because of the lower sensitivity.
Rules are expected to come down from several different sources, such as transportation authorities, health insurance companies and employers that require some form of accurate indication of when a MAD device is being worn. Current devices that use temperature only can be easily fooled. Similarly devices that rely on temperature only will have issues in functioning properly in warm environments. A compliance monitoring system that checks only whether the intra-oral temperature is within an acceptable range is easily deceived by creative individuals, for example, by placing it in a warm water bath, kept at a constant temperature with a heating device and thermostat during sleeping hours.
For example, Rahman et al. (US2006/0166157 A1) teaches a device that may use a combination of temperature, moisture, pH, light, and pressure measurements to make it more difficult to deceive the system. DuHamel et al. (US2010/0152599) teach an oral appliance that uses measurement of blood-oxygen saturation levels in the oral tissues to more accurately verify compliance. Abolfathi (U.S. Pat. No. 7,553,157 B2) teaches the use of a colorant indicator that reacts to temperature, moisture, and/or one or more intra-oral chemical or biological species. However, these additional measurements not only consume additional power, but in many cases, also involve different mechanical requirements, such as small openings to allow direct contact with the oral cavity and/or tissues, as is the case with pH, moisture, and species measurements. These openings are at risk of bacterial contamination which may then infect the patient.
Longley (US2007/0283973) teaches an oral appliance that responds to commands received via a transceiver to record measurements such as temperature, hydrogen ion concentration, pH, moisture, absolute humidity, or movement of oral appliance at periodic intervals. The recorded measurements are analyzed to determine if the measurements are consistent with the conditions expected in the oral cavity. Additionally, the recorded measurements are used to determine usage patterns as well as to determine if the user's use of the oral appliance has been in accordance with a patient's prescribed therapy schedule.
However, the above-described methods are susceptible to deception by users placing the dental appliance in artificial environments that mimic conditions in the oral cavity. The method of the present invention is devised to be difficult to deceive without requiring significant additional power and increasing the size of the device.